The present invention relates generally to two stroke, opposed piston engines and, more particularly, to compression release brake arrangements and methods for such engines.
In conventional diesel engines that have a single piston per cylinder, a compression release braking function or engine retarder brake can be achieved by opening the exhaust valves at the top of the compression stroke, resulting in adiabatic expansion of the compressed air, so the large amount of energy stored in that compressed air is not returned to the crankshaft, but is released into the atmosphere, http://en.wikipedia.org/wiki/Engine braking Normally during the compression stroke, energy is used as the upward-traveling piston compresses an in the cylinder; the compressed air then acts as a compressed spring and pushes the piston back down. However, with the engine retarder brake in operation, the compressed air is suddenly released just before the piston begins its downward travel. Having lost the energy stored within the compressed air, there is no ‘spring back’ from it so the engine must expend yet more energy pulling the piston back down again.
In typical opposed piston engine designs, it is not possible to open an exhaust valve at the top of the compression stroke because an exhaust port in the cylinder wall is closed by the exhaust piston. Accordingly, it is desirable to provide an apparatus and method for performing a compression release braking function in a two stroke, opposed piston engine.
In accordance with an aspect of the present invention, a two-stroke, opposed-piston engine comprises a cylinder including an inlet port and an exhaust port, an inlet piston movable in the cylinder between an inlet piston top dead center (IPTDC) position and an inlet piston bottom dead center (IPDBC) position, an exhaust piston movable in the cylinder between an exhaust piston top dead center (OPTDC) position and an exhaust piston bottom dead center (OPBDC) position, a charge air channel in fluid communication with the inlet port, a combustion chamber defined by the cylinder, the inlet piston, and the exhaust piston, the inlet piston permitting flow communication between the inlet port and the combustion chamber when the inlet piston is in the IPBDC position and blocking flow communication between the inlet port and the combustion chamber when the inlet piston is in the IPTDC position, the exhaust piston permitting flow communication between the exhaust port and the combustion chamber when the exhaust piston is in the OPBDC position and blocking flow communication between the exhaust port and the combustion chamber when the exhaust piston is in the OPTDC position, a conduit extending directly from the combustion chamber to the charge air channel, and a valve arranged to selectively open and close flow communication through the conduit.
In accordance with another aspect of the present invention, a two-stroke, opposed-piston engine comprises a cylinder with an inlet piston controlled inlet port and an exhaust piston controlled exhaust port, the cylinder defining a combustion chamber with the inlet piston and the exhaust piston, a charge air channel in flow communication with the inlet port, a conduit extending directly from the combustion chamber to the charge air channel, and a valve arranged to selectively open and close flow communication through the conduit.
In accordance with yet another aspect of the present invention, a method of operating a two-stroke, opposed-piston engine is provided, the engine comprising a cylinder with an inlet piston controlled inlet port and an exhaust piston controlled exhaust port, the cylinder defining a combustion chamber with the inlet piston and the exhaust piston, and a charge air channel in flow communication with the inlet port. The method comprises selectively opening and closing flow communication through a conduit extending directly from the combustion chamber to the charge air channel.